The devices and related methods of the invention relate to the controlled introduction and removal of fluids in diagnostic, therapeutic and imaging applications within the body. Specifically, the invention relates to the advantageous use of a fluid exchange device in combination with a catheter to produce a system for controlled aspiration and irrigation and the selective and localized exchange of fluids within a body conduit, for example, in the diseased region of a blood vessel having a blockage or lesion. The devices of the invention, and the methods enabled by the use of the devices, have several different components that can be used individually or integrated into a system for use within an organ and within the vasculature of the body where controlled and localized irrigation and aspiration are performed together as a therapeutic procedure or in tandem with a separate therapeutic procedure.
Irrigation and aspiration are clinically important in many surgical procedures when fluids are selectively introduced into and removed from a target site within the body, usually while a surgery or other therapeutic medical procedure is performed. When the site of the therapeutic treatment is inside a body cavity or in the vasculature of the body, such as in a blood vessel, the irrigation and aspiration functions require special apparatus and methods. Surgical and percutaneous systems that both irrigate and aspirate have been developed, and some of these systems are catheter-based such that the introduction and removal of fluids is performed within an organ or a vessel by using the catheter as the conduit to introduce and remove fluids from a target site. As will be readily appreciated, the catheter allows the control elements to be remotely located, e.g., outside the body while the actual irrigation and aspiration functions are selectively provided within the body by selectively orienting the distal end of the catheter to the target site. In such cases, as is the case in open surgeries, the irrigation and aspiration functions accompany a therapeutic procedure that is performed at the target site along with the irrigation and aspiration.
Catheter-based irrigation and aspiration systems are unique in many respects due to their use in clinical situations where blockages or lesions exist inside a blood vessel, such as a coronary or carotid artery, and dangers arise from the creation and release of emboli within the vessel. In many intravessel therapeutic procedures, the danger from the creation of emboli is an unavoidable aspect of the therapeutic procedure. For example, lesions of atherosclerotic plaques inside a blood vessel are treated by several therapeutic procedures including endarterectomy, atherectomy, the placement of intravessel stents, balloon angioplasty, surgical ablation of the lesion, thrombectomy, OCT, dialysis shunt clearing and others. However, while each of these procedures has great therapeutic value in treating the lesion, each carries the risk of creating emboli during the procedure. As with any procedure conducted in the cardiovascular system, the risk is particularly great where plaque dislodged from inside a blood vessel can travel to the brain causing serious brain injury or death. For example, treating lesions of the carotids necessarily involve high risk. Currently, carotid treatments are attempted together with deployment of a filter to attempt to track emboli generated by or released from a carotid lesion. Unfortunately, crossing a carotid lesion with a filter or other structure can generate a cerebral ischemia or stroke. Schlueter et al. 2001, Circulation 104 (17) II-368. Moreover, studies have shown that merely crossing a carotid lesion with a guide wire can generate emboli. Al-Mubarak et al.: Circulation 2001 OCT 23:104 (17): 1999-2002. Also, some lesions carry such a high risk of generating emboli that therapeutic treatments are attempted only in the most severe cases. Where a chronic total occlusion exists, the diagnosis is particularly poor because it is impossible to place a structure distal of the occlusion such that emboli generated by the removal of the occlusion can be captured before circulating in the bloodstream. Such occlusions can only be treated by removing the occlusion from the proximal side, where emboli removal is uniquely difficult. Accordingly, if the capability existed to dramatically reduce the dangers of emboli creation during therapeutic procedures inside a vessel or organ of the body, the existing procedures would be safer and more widely practiced, and new procedures would be performed.
A variety of systems to contain and remove emboli have been proposed wherein a portion of a vessel that contains a lesion is segregated by two occluding members, typically two balloons, which are inflated proximate and distal to the lesion to effectively seal the inside of a region of the vessel containing a lesion prior to treatment of the lesion. Once treatment is complete, embolic particles such as dislodged plaque are removed by applying suction between the balloons. However, the tissue affected by a lesion is notoriously delicate and the treatment of the lesion has the capability to generate or release emboli whenever any mechanical manipulation of the lesion occurs. The generation and/or release of emboli is a concern virtually anytime a structure is passed through a susceptible vessel. Such circumstances include the placement of a balloon or stent, the placement of a filter, or simply the use of a catheter or guide wire for imaging, diagnostic, or any other procedure. In many procedures, the internal portion of a vessel is occluded to provide a segregated region of a vessel through which fluid does not flow. Moreover, virtually anytime structures are inserted into the vessel, the generation of release of emboli is a concern. For example, in the common practice of placing a stent inside an artery, a filter may be placed distally of the stent to attempt to collect emboli generated when the stent is expanded to engage plaques or lesions inside the vessel. All devices placed distal involve the crossing of the lesion. All crossings of lesions create emboli of some quantity and significance. Such systems cannot protect the patient against the potential harm inherent in the placing the device. Additionally, once the stent is in place, the filter must be removed by pulling it through the portion of the vessel in which the stent has been inserted. This carries the risk that the filter will impact the vessel and cause the release of emboli and/or contact the stent and either displace the stent or similarly cause the release of embolic particles. The use of occluding members of any type has certain drawbacks. Anytime a structure is used as an occlusive member inside a vessel, the structure must deform the vessel from the inside to create a seal about the periphery thereof with the internal surface of the vessel. For example, to make the seal tight enough to prevent the passage of fluid and emboli past the balloon, the expansion of the balloon typically deforms the vessel outward and may disrupt plaque in and about the point of contact between the vessel and the balloon. Moreover, any plaque that becomes dislodged outside the barrier formed by the balloon is released into the blood stream because there is no mechanism distal of the balloon to remove the emboli. For this reason, irrigation and aspiration proximate to the lesion are particularly important.
To create a segregated region of a vessel, a two-balloon system may be used. However, certain disadvantages of a two-balloon system also arise from the placement of balloons on both sides of a lesion and the nature of the blood flow that occurs in the region of the vessel containing the lesion once the balloon is removed. At the point of contact between the balloon and the vessel, plaque may be compressed underneath the balloon and may become dislodged upon reestablishment of flow through the vessel. Furthermore, many clinicians have observed that the region distal of a lesion is more likely to exhibit plaque formation than the region proximal of a lesion. Thus, the use of an occluding member distal of a lesion does not eliminate the risk of creating emboli that may enter the vessel. The risk is particularly great when a second balloon is used because the balloon is not advantageously placed for the removal of emboli created by the use of the balloon itself and because the balloon must be removed by passing it across the lesion upon completion of a procedure. This drawback is present in all circumstances when a balloon is advanced across a lesion because, when any occluding member is placed distally of the lesion, the occluding member must be drawn back across the lesion to remove the occluding member at the end of a procedure. Each passage of an occluding member across the lesion, even in a retracted or deflated state, carries a substantial risk that additional emboli will be produced.
Also, the placement of two balloons requires additional time to inflate the second balloon and adds to the complexity of a device due to an additional lumen that must be incorporated into the catheter to inflate the balloon. In a finite number of cases, the occluding member that is distal of a lesion, and is required to retain emboli in a defined area within the vessel, has been observed to fail, thereby releasing the emboli into the bloodstream. Because the second balloon is relied upon to prevent the flow of emboli past the region of the vessel containing the lesion, the failure of the balloon is a critical event that threatens the health of a patient undergoing the procedure. Furthermore, due to geometric constraints, the second balloon often acts as the guide wire as well. When delivering tools to perform the therapeutic or diagnostic procedure within the vessel, the balloon may move and disrupt the vessel wall. Introduction of tools and other manipulations of a distally located balloon can also result in deflating the balloon or otherwise causing the balloon to lose patency on the interior of the vessel.
Anytime that a balloon is placed distal to a lesion, the contact between the balloon and the lesion carries the risk of damaging the vessel. For these reasons, the use of balloons inside the vessel is preferred to be minimized and the length of time and extent of contact between a balloon and the inside of a vessel should be reduced. Ideally, the balloon or other occluding member could be placed proximal to a lesion so that the area containing the lesion would be isolated. To achieve this, the irrigation and aspiration functions would have to be provided by a structure that is positioned distal of the occluding element, such that the occluding element could be placed proximal of the lesion, and the aspiration and irrigation functions achieved distal of the occluding member.
Even under existing technologies where aspiration and irrigation are applied in a catheter based system, the parameters of fluid flow, as well as the placement of the aspiration and irrigation ports relative to an occluding member, are important to the physiological outcome for any given procedure. For example, removal of fluid and/or embolic particles by simple suction from within a body conduit may only remove a portion of the fluid present in the vessel and may leave emboli in place even if all of the fluid is removed and replaced. Deposits of plaque and other debris that may exist inside a vessel have a tendency to adhere to one another and particulate emboli tend to adhere to the sidewalls of the vessel. Thus, a system that provides limited fluid exchange is particularly unlikely to achieve a complete removal of emboli. Also, given that the interior walls of a vessel may have been contacted from within during a therapeutic procedure, a high likelihood exists that additional particles may be dislodged upon the establishment of a robust fluid flow through the vessel.
Ideally, a system for aspirating and irrigating the interior or a vessel or organ would provide both fluid exchange and fluid flow parameters that are at least similar to that experienced during ordinary physiological functions and preferably would create a turbulent fluid flow that would proactively assist in the removal of particles and other emboli. Such a system would require both a catheter element that achieved aspiration and irrigation as well as a fluid exchange apparatus that would be coupled with the catheter to produce the desired fluid flow rates and other fluid parameters. Because of the wide variation in intravessel procedures and the location of disease, an irrigation and aspiration system would also be particularly useful if the catheter element could be selectively positioned along a specified length of a vessel where emboli may be created together with operation of the fluid exchange apparatus to control the irrigation and aspiration flow. This capability in the catheter element is most readily created with only a single balloon system having a separate, movable, irrigation and aspiration catheter.
In the prior art two-balloon system described above, where a region of a vessel is segregated by a pair of balloons located both proximally and distally of a lesion, the area of fluid flow is limited to the region defined by the placement of the two balloons. The problem is particularly acute when a vessel is treated with a procedure that installs a stent or manipulates the plaque in a vessel, such as with an angioplasty, where the lesion is physically manipulated as part of the therapeutic treatment. Assuming that the therapeutic treatment is successful, the vessel is treated by virtue of expanding the interior volume and promoting the flow of blood through the vessel. Under these circumstances, the portions of the vessel distal of the lesion have been contacted by a balloon and are then exposed to a higher volume of fluid flow than existed before the procedure. In the context of a typical patient, a vessel which had become slowly blocked due to the deposit of plaque over a large number of years has been expanded by the treatment of the lesion and this therapeutic treatment at an upstream point subjects the region in which the lesion is located and those downstream internal portions to a rate and volume of blood flow that has not been experienced in the many years since the vessel began to become occluded. Under these circumstances, an additional risk exists that plaques located downstream from the lesion will be dislodged and will enter the circulation causing serious injury.
As with ordinary irrigation and aspiration in an open surgery, the irrigation and aspiration that are applied through existing catheter systems are typically regulated only by setting the positive or negative pressure that is applied to the aspiration or irrigation lumen of the catheter and is in turn communicated to the distal end of the catheter to insert or remove fluid respectively. However, to create the specific fluid flow parameters that maximize the removal of emboli and the fluid displacement within a vessel, thereby establishing fluid change in the vessel in the most physiologically relevant manner, a specialized fluid exchange device would have to be created to regulate the fluid flow parameters of both the irrigation and aspiration functions of the system.
An ideal irrigation and aspiration system could be an additive component to several other apparatus that are used in therapeutic, diagnostic, or imaging applications in the body such that the capability of the system would not be exclusive of other technologies that have been applied to enhance the safety of an intravessel procedure. Several different approaches apart from irrigation and aspiration have been attempted to physically capture emboli downstream at a lesion, most notably through the use of filters. However, filters have inherent drawbacks that cannot be completely eliminated. For example, embolic particles smaller than the filter pore size, commonly on the order of 100 microns evade filters, which must not be so small that physiologically important elements such as red and white blood cells are captured by the filter. Also, particles larger than the pore size tend to become trapped in the filter such that the filter itself becomes an occlusive element and blood flow through the filter is impeded. Also, as described above for occluding structures, whenever a filter is introduced distally to the lesion in a vessel, a finite probability exists that the removal of the filter will generate emboli. Still further, where a stent is placed at a lesion, the movement of the filter past the stent and through the vessel has the capability to catch or displace the stent.
Although certain portions of the discussion herein are directed towards a preferred embodiment of the apparatus of the invention used in an intravessel procedure, the devices and methodologies of the invention can readily be applied to non-vessel sites within the body such as within any body conduit such as an ear canal, colon, intestine, the trachea, lung passages, sinus cartilages, or any internal volume wherein a controlled and localized irrigation and aspiration function are desired. For example, in a diagnostic colonoscopy an endoscope may be introduced to aid in optical visualization of the site. However, the colon responds to fluid pressure changes and thus while trying to clear the field the tissue of note may move. To aid in this diagnostic situation, a controlled introduction of a clear fluid could be introduced in concert with an equivalent aspiration of dirty fluid. As such, the tissue may remain in the field of view while the process occurs. For imaging purposes the introduction of a contrast agent while simultaneously extracting an equivalent fluid will allow a vessel or organ to maintain its normal fluid level and pressure. As the imaging is completed, the same system could then return a more normal fluid to the site while extracting the foreign contrast agent. Imaging xe2x80x9cpig-tailxe2x80x9d catheters are presently used to introduce contrast agents to vascular system, even though radiopaque contrast agents are known to maintain a level of toxicity (Solomon, Kidney International, 1998, vol. 53, pp. 230-242). If the field of contrast was introduced and extracted as proposed by Courtney, et al., the patient""s exposure would be substantially reduced.
The present invention provides control of both irrigation and aspiration functions at a selected location within a body cavity or conduit, such as a target region of a blood vessel. The region of the vessel to which an irrigation and aspiration function are provided may include both a therapeutic treatment site, the site proximal to the placement of a balloon, or a length of a vessel both proximal to and distal of a lesion wherein a surgical treatment was performed, where a diagnostic or therapeutic procedure caused the insertion of a dye or other solution, such as a clot dissolver, or where a total chronic occlusion occurs. Because the irrigation and aspiration functions are performed simultaneously, the fluid exchange apparatus of the invention is able to simultaneously regulate both irrigation and aspiration in a manner that advantageously controls the fluid flow rates and fluid flow parameters. This capability can be achieved both by controlling the flow rates using an electronic control system, as well as providing a mechanical apparatus that controls irrigation and aspiration flows when actuated by a user. When the catheter and fluid exchange device are combined into the system of the invention, the combination provides unique capabilities for treating or diagnosing a lesion contained within a vessel. For example, the lesion may be pre-treated prior to the therapeutic treatment which typically comprises ablation of a lesion or placement of a stent or expansion of the diameter of the vessel, i.e., through an angioplasty procedure. In a diagnostic embodiment, dye or other diagnostic markers can be infused distally of the occluding member and proximate to the lesion while avoiding the potential hazards of passing a collapsed balloon across the lesion. This provides a diagnostic capability which has substantially reduced risk relative to a therapeutic treatment that requires expansion of an occluding member distal of the lesion. Because of the added safety margin, the diagnostic procedures can be more readily performed without the risk of producing emboli and thus are a more available complement to the therapeutic procedure.
Preferably, the system of the invention includes a catheter element having specific features designed to facilitate the desirable fluid flow parameters when connected to the fluid exchange apparatus. Ideally, when coupled with an apparatus that inherently provides controlled and regulated fluid flows for both aspiration and irrigation, the catheter works in tandem with the apparatus to create both controlled and localized irrigation and aspiration through a catheter-based system. For example, the apparatus of the invention allow the user to control the irrigation and aspiration flow volumes, and by virtue of a specially designed catheter system, provide improved fluid flow parameters that facilitate quantitative volume exchange within a vessel or other cavity and produce defined fluid flow parameters in a region bordered by an occluding element. Accordingly, the aspiration and irrigation functions provided by the fluid exchange device can be added to several existing devices such as balloon occluding elements or filters, or can be used alone as a catheter-based fluid exchange system without any additional device. Thus, the fluid exchange capabilities can be added to an existing device such as a straight catheter or filter, or an existing device can be integrated into the remaining components of the present invention to provide the advantageous irrigation and aspiration functions as described herein. For example, to decrease time during a therapeutic or diagnostic procedure, the portion of the catheter element providing the irrigation function could be combined with a catheter used to perform an angioplasty procedure.
When so integrated, the irrigation and aspiration functions of the invention are located distal to the angioplasty balloon and the enhanced removal of emboli is facilitated. Also, the location of the irrigation and aspiration lumens can occur such that the aspiration ports are on opposite sides of an occluding member or other structure such that a direct irrigant to aspirant volume exchange may or may not occur in the lesion of a vessel. In preferred embodiments of the system of the invention, the catheter element provides turbulent, rather than laminar, flow within the vessel. Turbulence is introduced locally at the region of fluid exchange within the body. In a turbulent flow, the velocity at a point fluctuates at random with high frequency and mixing of the fluid is much more intense than in a laminar flow. Turbulent flow is specifically preferred because it reaches the walls of a body structure and facilitates both fluid exchange and dislodging of particulate matter. To reach the walls, the irrigation ports exit the catheter element in the direction of the wall. To accomplish this, the catheter element preferably has ports that exit orthogonal to the wall of the distal end of the irrigation lumen of the catheter. The aspiration lumen may establish a local laminar flow profile. This results in laminar flow about the vessel.
Also, in a turbulent flow, the velocity at a point fluctuates at random with high frequency and mixing of the fluid is much more intense than in a laminar flow. This is of particular value when attempting to clear any site of debris. Without turbulence, the flow along the sides of a vessel/lumen is approximately 0. When trying to remove/clear or exchange fluids thoroughly is it imperative to facilitate mixing. Mixing can only reach the vessel walls through the application of turbulence. This is appreciated by the vessels as well, since turbulence can be achieved with this invention without high-powered injection systems that carry physiological risks associated with their inherent power and abnormally high flow rates.
In more scientific terms, when a laminar flow is made turbulent, then the velocity will become more uniform and higher, and as a result, fluid particles in the boundary layer can move farther downstream before separation takes place. This turbulence is generally local to the irrigation area and controlled by the dimensions and orientation of the ports of the irrigation lumen.
The flow and velocity exchange rate through the entire system is not altered significantly since the turbulence is local area around the irrigation ports. But turbulence for an equivalent flow produces a much more uniform flow across the vessel. This results in higher velocities along the wall where emboli and thrombus are known to be in residence. From a physiological relevance standpoint, blood clots, or thrombi, are much more likely to be released into turbulent than in laminar flow. (Berne and Levy, 2001, Cardiovascular Physiology, p. 126).
Because flow is proportional to viscosity, irrigation with any number of fluids can increase the flow over just aspiration of the site. For example, the viscosity of blood is 5 times that of water in a vessel larger than 0.3 mm in diameter, (from graph 5-14, in Berne and Levy, p. 129). The resulting combination of turbulence and the introduction of various fluids allows for substantially variable fluid flows which cannot be achieved without the combination herein disclosed.
Those of skill in the art will appreciate that the fluid exchange capabilities and fluid flow parameters provided by the invention can be integrated into a number of systems to provide irrigation and aspiration and essentially any physiological context where near quantitative removal of fluid or particles from a site is desired. As noted above, the enhanced fluid flow parameters can be strategically oriented relative to the placement of an occluding member, such as a balloon, to effectively remove fluids or solid matter either proximal to or distal of the occluding device. The catheter element of the apparatus can also be positioned to facilitate the removal of dyes, or therapeutic or diagnostic compounds as part of the fluid exchange function of the apparatus of the invention.
In a preferred embodiment, the invention provides both irrigation and aspiration in a selected region of a vessel proximate to a lesion, but without any occlusion distal of the lesion such that the occluding element may be both inserted and removed without passing across the lesion. Because of the design of the catheter-based system, a single catheter element may both aspirate and irrigate and may be moved within the vessel whether or not used in combination with other apparatus. When used in combination with an occluding element, the irrigation and aspiration factors may be fixed in place proximate to a lesion within a vessel or may be movable such that a single catheter element having both aspiration and irrigation functions can be advanced into an area proximate a lesion and actuated to perform the irrigation and aspiration function both proximate to the lesion and distal to the occlusion element. Similarly, if there exists a distal device (filter or occlusion balloon) this system can be activated to accomplish the following optimum clinical benefit. The irrigation ports being just proximal, but not exclusively proximal, to the aspiration port, then the vessel can be irrigated actively with the local flow moving prograde. This drives the emboli up against a more distal occluder/filter and there the aspiration port evacuates the emboli. Used in concert with existing filters or balloons this results in optimum retrieval of emboli from the active irrigation. This embodiment does not require a proximal occlusion for clinical benefit.
In procedures where emboli may be present, this device may be used as part of a method to extract the emboli generated during either a therapeutic, surgical, imaging or diagnostic procedure. The volume exchange provided by the current invention is also adapted to facilitate removal of fluids within a measured portion of a vessel where vessel dimensions and fluid volumes are known. This device affords a simple mechanical means through which these may occur in concert. Primary applications have been identified that produce a 1:1 exchange of fluids, but further applications include pulsatile exchange rates and ratios other than 1:1.
The control aspect of the invention is derived in part from measured volumes that may be inserted and removed through a catheter system comprising an irrigation lumen and an aspiration lumen in fluid communication with irrigation and aspiration port(s) that insert and remove a defined or predetermined volume of solution. The design of the catheter and the fluid flow parameters achieved at the target site produce specific fluid dynamics within a vessel or body conduit that promote the removal of emboli and/or the near quantitative removal of a fluid contained in the region of a body conduit. In a preferred embodiment, a catheter coupled to a fluid exchange apparatus is actuated to create turbulence within the vessel or organ and proximate to the ports or exit holes of the irrigation lumen. As described in detail below, the size and orientation of the ports and lumen changes the fluid flow parameters such that defined flow rates, volumes, vortices, turbulence and ratios of fluids exchanged within the body can be custom designed for any application, vessel, or organ, as well as for specific diagnostic, therapeutic or imaging applications. Because many of the embodiments of the invention are used within the cardiovascular system, the irrigation and aspiration function can be designed such that fluids move into the vasculature in a pulsatile manner as with the movement of blood within the vessel caused by the beating heart. This type of fluid movement and fluid exchange provided by the aspiration and irrigation functions of the invention is advantageous because the insertion and removal of fluid in this manner exposes the vessels or other structures to fluid flow that is physiologically relevant. In the sense that the vessel experiences fluid flow that is similar to that experienced after the therapeutic, diagnostic, or imaging procedure is performed and any emboli that would be released following the procedure are more likely to be released during the irrigation or aspiration process performed by the devices of the invention.
As described in more detail below, the design also facilitates a defined fluid exchange rate, such as 1:1 volume exchange that avoids damage to the vessel while producing turbulence to facilitate the removal of emboli. Generally, turbulent flows provided by the device of the invention are localized and controlled in both volume and location and are typically higher than that provided by the existing devices in terms of both flow and velocity. Target flows of 1 cc/sec are relevant to vessels such as the vein grafts, flows up to 2 cc/sec are relevant for vessels such as the carotids. (Louagie et al., 1994, Thorac Cardiovasc Surg 42(3):175-81; Ascher et al., 2002, J Vasc Surg 35(3):439-44).
As noted above, an advantage of the invention is the generation of localized turbulence in the vicinity of the infusion catheter such that volume exchange within the vessel promotes the disruption of embolic particles that are only loosely attached to the interior walls of a vessel. This advantage is derived from both the design of the catheter, which affects the location in which fluids are inserted and removed into a vessel or an organ, as well as the specific design and function of the fluid exchange apparatus that, when coupled with the catheter of the invention, combine to produce improved fluid exchange and fluid flow parameters. For example, in an ordinary vessel that is roughly cylindrical within a defined axial distance along the length of a vessel, the removal of liquid generally produces a laminar flow through the center of the annular structure of the vessel and the fluid along the walls of the vessel are largely left in place. With a turbulent fluid flow profile, the fluid introduced into the vessel causes an exchange between the irrigant the existing fluid that is localized along the vessel walls and generally causes a more thorough mixing of the fluids within the vessel such that a more complete fluid volume exchange occurs and the removal of embolic particles is enhanced.
Although the particular parameters vary according to the designs described below, the fluid exchange achieved by the fluid exchange apparatus and the irrigation/aspiration catheter results in an insertion and removal of a defined volume within a vessel. As described in further detail below, the overall system is comprised of a fluid exchange apparatus that may have a mechanical or electrical, or both, fluid exchange component that converts a defined volume of fluid exchange with a defined axial movement of the catheter such that the volume of fluid exchanged per measure of distance of axial movement of the catheter through a vessel is known. Preferred embodiments of the fluid exchange apparatus are a substantially closed system wherein a reservoir containing irrigating fluid is combined with a reservoir containing the aspirated fluid such that known volumes are exchanged through a system that is essentially xe2x80x9cclosedxe2x80x9d except for the exchange site within the vessel. The terms xe2x80x9csubstantially closedxe2x80x9d mean that the system is closed because the volume of fluid inserted as irrigant solution is removed as aspirant solution in a predetermined ratio and any deviance from the ratio is attributed to only a volume of solution that is retained within the body at the target exchange site. For example, when a system of the invention is applied to irrigate and aspirate fluid from within a vessel, the system is substantially closed because the only difference between the fluid inserted as irrigant and removed as aspirant is that which is purposefully left behind in the vessel. When the volume exchange ratio of the device is set at a 1:1 ratio, the volumetric exchange of fluids is very near to equivalent. The fluid exchange apparatus may also be actuated in such a manner that the flow produced by actuating the fluid exchange apparatus is a defined increment. Thus, a known volume of fluid is exchanged at the target site and the clinician knows with certainty the volume of irrigant fluid that is inserted as well as the volume of fluid that is aspirated out of the target site.
In one embodiment, the device of the invention provides a 1:1 ratio of irrigation to aspiration fluid exchange such that the volume of fluid introduced to a vessel or organ is exactly matched by the volume removed. Through control of the location and movement of the device of the invention, the interior of a vessel or organ can undergo a complete fluid exchange by advancing the infusion catheter along the length of a vessel where removal of fluid is desired. By this process, several results are achieved that are beneficial therapeutically. First, the vessel experiences a turbulence and a fluid flow that is physiologically relevant in the sense that both the volume of fluid moving across a vessel as well as the turbulence are similar to the parameters that the vessel would experience under blood pressure. This similarity has several aspects. First, the turbulence that occurs in a vessel is similar to the turbulence caused by the motion of blood moved by a beating heart. Second, the pulsatile nature of the fluid exchange is also similar to the varying pressures and pressure profile caused by ventricular contraction and the ordinary movement of blood throughout the arterial system. Finally, these specific fluid flow characteristics are achieved without producing substantially increased pressures within a vessel and without distending the vessel through the application of increased fluid pressures. Thus, the combined irrigation and aspiration of controlled volumes of liquid treat the vessel with a physiologically relevant fluid profile.
Because the device of the invention offers the ability to introduce and remove a defined volume of fluid, the clinician can have a high degree of certainty that the entire internal volume of a region of a vessel has been rinsed with an irrigation fluid by knowing the approximate internal volume of the vessel and the length of the vessel in which irrigation and aspiration are performed. For example, assuming that a specified region of a vessel has an internal volume of 20 ml over a defined axial length. The device of the invention can be used to insert predetermined volumes of solution greater than, less than, or equal to 20 mls over the defined length of the vessel. Depending on the clinical environment, the ratio may be altered to remove greater volume by establishing a smaller ratio of irrigation to aspiration. One could, for example, irrigate with one volume of solution while removing twice the volume through the aspiration portion of the system to yield a 1:2 irrigation to aspiration volume.
In a preferred embodiment, the fluid exchange device has the ability to perform a controlled exchange of fluid with predetermined ratios including a 1:1 irrigation to aspiration ratio and varying ratios particularly values ranging between a 1:2 irrigation to aspiration ratio and a 2:1 irrigation to aspiration ratio. Preferably, this is achieved by having irrigant and aspirant reservoirs of defined volumes built into the fluid exchange device. However, the device can also feature a selectable control that alters the ratio of fluid exchange between a minimum and a maximum as a function of the operation of the device. In the mechanical embodiment of the fluid exchange device, each actuation of the device may cause a defined volume of fluid to be propelled through an outlet that is in fluid communication with the irrigant lumen of a catheter element. In combination, the device also features an aspirant reservoir which is expanded by a predetermined volume relative to the volume of the irrigant that is expelled.
The control of these parameters, in some aspects, by the fluid exchange device is the result of designing the fluid exchange device to cooperate with both conventional catheters as well as those specially designed to produce turbulent flow at the target fluid exchange site. The fluid control functions of the exchange device can also cooperate with the catheter element by incorporating the capability for the fluid exchange device to control motion of the catheter, specifically axial movement within a body conduit such as a blood vessel. In this embodiment, the catheter element is coupled to the actuation of the fluid exchange device by a coupled translation mechanism wherein, as described in further detail below, each actuation of the device results in automatic advancement or retraction of the catheter. Thus, a defined exchange of fluid volume at the target site occurs in combination with advancement or retraction of the aspiration and/or irrigation element of the catheter by a defined distance. In this manner, repeated actuation of the device provides a step-wise motion of the irrigation and evacuation functions and can insure a near quantitative volume exchange over a defined distance. As will be apparent from the following description, this aspect of the invention provides the ability to insert and/or remove a defined volume of fluid distal of an occluding member given an approximate knowledge of the dimensions of the vessel. As with the other embodiments, the operation of the system may provide fluid exchange with a pulsatile fluid flow by virtue of the application and dissipation of pressure achieved through the catheter.
Any number of designs for the fluid exchange apparatus can be used to provide controlled volumes of irrigation and aspiration fluids, through the catheter element of the invention to the target exchange site. The simplest embodiment of the invention provides a squeeze bulb wherein the irrigant and aspirant reservoirs are typically separated by a membrane and are in fluid communication with a irrigation and aspiration lumen that communicate fluids to and from the target site. In this embodiment, a one-way valve is provided preferably on both the irrigant and aspirant side of the fluid flow, to prevent aspirated fluid from flowing back to the target site. In another embodiment, a mechanical device causes pressure to be exerted on an irrigant reservoir that is in fluid communication with an irrigation lumen that provides fluid flow to at least one irrigation port at the distal end of a catheter. The catheter element also comprises an aspiration lumen, that may or may not be integral with the irrigation lumen, and which facilitates fluid communication of the aspirant fluid back to an aspirant reservoir. In this embodiment, the irrigant is expelled from a reservoir by the application of mechanical force to reduce the volume of the irrigation reservoir and the mechanical force is preferably coupled to an expansion of the volume of the aspirant reservoir to yield a defined fluid exchange between the irrigant reservoir and the aspirant reservoir.
Those skilled in the art of medical devices will appreciate that all of the component parts of the invention are assembled from biocompatible materials, typically medical plastics or stainless steel. The syringes described below may be ordinary medical-use syringes or may be custom fitted to be replaceable and to fit engagingly with the fluid exchange apparatus. An irrigant reservoir that is integral with the device may be pre-filled or a pre-filled syringe may be used to supply the irrigant fluid. In either a stainless steel or plastic embodiment, the device is stabilized. Typically, stainless steel devices are exposed to heat and steam in an autoclave, while medical plastics may be exposed to gamma irradiation or microbicidal gases such as EtO. The methods of the invention specifically include the use of any component of the system of the invention followed by sterilization of the components, or the entire system, and re-packaging for subsequent use. Although plastic embodiments are designed for single use, sterilization may be performed to functionally reconstruct the utility of the device after use with a patient.
In one preferred embodiment, a hand-held mechanical device is actuated by a trigger to insert and remove controlled volumes of fluid through the catheter element. The hand-held embodiment is comprised of an actuator such as a movable trigger that is mechanically operated by being grasped by the hand and pulled towards a stationary structural housing of a complementary portion of a housing to cause a reduction in the volume of an irrigant reservoir and, accordingly, fluid movement through an irrigation lumen and out one or more irrigation ports at the distal end of a catheter. Fluid provided to the target site in this manner is recovered through one or more aspiration ports and communicated through an aspiration lumen and returned to the aspirant reservoir of the fluid exchange device. The irrigant and/or aspirant fluids are preferably contained in a sealed reservoir system such as a cylindrical chamber having a piston and a rod wherein the piston is mechanically coupled to the actuating element. Motion of the actuating element transfers force to the piston and causes contraction of the irrigant reservoir and expulsion of liquid from the reservoir. Simultaneously, the motion of the actuator causes the expansion of the volume of the aspirant reservoir and causes withdrawal of fluid through the aspiration lumen and into an aspirant reservoir. In such an embodiment, the actuation of the trigger may translate into varying amounts of fluid flow depending on the mechanical expedients used. A single actuation of the trigger may translate into an incremental movement of a piston that exerts force on an irrigant and/or aspirant reservoir. By the use of several conventional mechanical apparatus, such as a ratchet and gear mechanism, a lever and pivot system, or others, the mechanical fluid exchange device exerts a direct control over the exchange of fluid communicated through the irrigation and aspiration lumens. The control of the fluid and the particular features can be provided in several designs that achieve the same function. For example, in addition to the hand-held apparatus described below, the force needed to create the fluid flow in both the aspiration and irrigation sides of the system could be provided by a mechanical foot pump, vacuum pump or virtually any component device that provides controllable fluid flow. Moreover, to provide total reproducibility in the operation of the system, a console controlled by a computer with appropriate commands or a software program is readily used to produce the same fluid flows, fluid exchange parameters, including exchange ratios, and essentially all of the functions of the purely mechanical embodiments described below. Therefore, those of ordinary skill in the art will appreciate that any number of mechanical or electrical variations give rise to the same fundamental principle wherein controlled volumes are applied to a target site through a segregated irrigation and aspiration system, preferably comprised of irrigation and aspiration lumens that pass through at least one catheter element and engage in fluid exchange at a target exchange site by virtue of specially designed irrigation and aspiration ports at the distal end of the catheter element.
By altering the dimensions of the irrigation reservoir and the aspiration reservoir, the ratio of fluid exchange between the irrigant and aspirant reservoirs is altered and, accordingly, the fluid exchange in the target vessel is adjusted. For example, where the irrigant reservoir and aspirant reservoir are of identical sizes, an actuation of the fluid exchange device may yield a 1:1 fluid exchange within the target vessel. Where, as described above, a different fluid exchange ratio is desired, the difference in the ratio may be achieved by a corresponding difference in the dimensions of the irrigant and aspirant reservoirs that are emptied and filled through the operation of the fluid exchange device. Also, variations in ratio may be accomplished by corresponding changes in the dimensions of in-line chambers as described below. Likewise, with a 1:1 ratio, equal volumes of irrigant and aspirant are exchanged in a single cycle of the fluid exchange apparatus. In the 1:1 embodiment, the entire irrigation and aspiration volumes may be exchanged within a defined number of cycles of the apparatus. For example, one may provide that each cycle of the hand-held apparatus provides 1 ml of irrigant volume and removes 1 ml of aspirant volume. By providing an irrigation and aspiration reservoir with known volumes, a known number of cycles translates into a known volume of irrigation and aspiration. As noted above, in one specific embodiment, the actuation of the device also causes translation of the infusion catheter along a defined axial path such that a known volume of solution is provided in both the irrigation and aspiration aspects as a function of the distance that is traveled by the infusion catheter.
Clearly, the irrigation reservoir may advantageously be divided into subparts and is not limited to ordinary aqueous solutions used in a surgical context. Given the utility of the present device for diagnostic and imaging applications, the irrigation reservoir could be filled with dyes, contrast agents, or other solutions that aid in the diagnosis or treatment of the vessel. Given that the fluid exchange device of the invention also provides unique fluid flow parameters, the irrigation reservoir could contain therapeutically valuable solutions such as heparinized ringers lactate, streptokinase, urokinase, tissue plasminogen activator, or other thrombus or emboli treatment fluids that are used to perform the therapeutic procedure on the internal portion of a vessel or organ. Given the ability to specifically tailor the fluid exchange parameters for a target vessel, the device offers the ability to use therapeutic compounds that might not otherwise be available because the clinician can be certain of the enhanced ability to remove solutions introduced via the irrigation reservoir. The fluid exchange apparatus can also be used to promote absorption of a therapeutic layer on a vessel wall. If a drug coated stent is produced that can reabsorb drugs after they have eluted, then with this device a high concentration of the drug can be introduced and pooled about the stent for a brief period. This high dose may then be absorbed or bonded back to the structure or one of its components and thereby recharging the drug coated stent.
Finally, in a system where it may be advantageous to have ratios other than 1:1 in the system it is also directly applicable. For example, in another vascular situation a virtual shunt may be created where a proximal fluid can be circulating and a fluid is infused distally. This would involve a ratio of greater than 1:1 irrigation to aspiration. Furthermore such an arrangement could introduce a second fluid to be the primarily distally delivered fluid. The second fluid could be blood, blood substitute, plasma or oxygenated fluid to produce a virtual shunt.
In the diagnostic use of optical coherence tomography, OCT, the fields of applications are presently limited by the need for a clear field. Similarly the use of intravascular ultrasound, IVUS, is somewhat limited by the attenuation associated with the blood in vivo. A substantial volume exchange of the vessel region in proximity of the distal end of the OCT or IVUS catheter would provide the opportunity to replace blood or other fluids with transparencies other than that found in blood, thus improving and/or modifying the imaging quality.